A method for suppressing the ripple current of a capacitor in a power conversion device has been proposed in the prior art (see, for example, PTL 1). Specifically, the prior art described in PTL 1 discloses the following technology.
In other words, a switching reference signal set to a prescribed phase difference is used in a plurality of inverter sections, to control switching of low potential-side switching elements and high potential-side switching elements corresponding to respective phases. Furthermore, in at least one of the plurality of inverter sections, the neutral point voltage, which is the average value of the voltages applied to each phase in the coil group of the rotary machine, is controlled in accordance with the phase difference, in such a manner that the center of a zero-voltage vector generation period, which is the timing at which either the low potential-side switching elements or the high potential-side switching elements are all on and the other thereof are all off, is displaced with respect to the zero-voltage vector generation period in the other inverter section. By controlling the voltage in this way, the ripple current in the capacitor is reduced.
Subsequently, when the duty ratio calculated by the control unit is equal to or lower than a first prescribed value, the vibration and noise are reduced by controlling the neutral point voltage so as to be half the capacitor voltage applied to the capacitor.